It is well known that cutting tools generate temperatures that are high enough to limit the life of the tool, thereby reducing the effective useful cutting speed. The temperature that is generated during cutting or forming depends on the frictional properties between the tool and the work material. The wear rate can be reduced and the performance of cutting tools can be improved by reducing friction which, in turn, reduces the temperature.
Transition metals such as titanium, vanadium and chromium (elements from groups IVa, Va, VIa in the Periodic Chart) form compounds with the elements boron, carbon, nitrogen and oxygen. These refractory compounds have been commonly used as coatings for cutting tools since they possess excellent properties for coatings (e.g., high temperature strength (hardness), abrasive wear resistance, extreme chemical stability and limited solubility in the work material). When these refractory materials are used alone as a coating for a cutting tool, they do not necessarily possess lubricious properties.
Molybdenum disulfide has lubricious properties. U.S. Pat. No. 5,002,798 to Donley et al. and U.S. Pat. No. 4,975,340 to Suhr et al. each disclose a method to produce a molybdenum disulfide film.
U.S. Pat. No. 5,965,253 to Rechberger et al. appears to disclose the use of a molybdenum disulfide layer on a cutting tool. Although in very general terms, the Rechberger et al. Patent seems to suggest at Column 4, lines 48-51 thereof the use of a molybdenum disulfide layer on the surface of a hard material (e.g., carbides, nitrides, carbonitrides and oxides).
U.S. Pat. No. 5,707,748 to Bergmann (and U.S. Pat. No. 5,830,531 to Bergmann) appears to disclose the use of a hard layer on the cutting tool and a friction-reducing layer on the hard layer. Bergmann suggests the use of carbon or carbides (e.g., tungsten carbide, chromium carbide, silicon carbide and titanium carbide)/carbon combinations. U.S. Pat. No. 4,992,153 to Bergmann appears to disclose the method of applying the coatings of the Bergmann patents (U.S. Pat. Nos. 5,707,748 and 5,830,531).
U.S. Pat. No. 6,284,366 B1 to König et al. appears to disclose a cutting tool that has a hard layer next to the substrate. An outer layer of molybdenum disulfide is on the hard layer. A thin metallic film (e.g., titanium carbide, titanium carbonitride, zirconium carbonitride) can be on the molybdenum disulfide layer. In the alternative, the molybdenum disulfide layer may be multi-layer with alternating layers of molybdenum disulfide and a metallic film.
PCT Patent Publication No. WO 00/55385 to Teer et al. [entitled METHOD AND CUTTING TOOL FOR CUTTING OF WORKPIECES] discloses a coating for cutting tools that possesses lubricious properties. The top coating layer is a carbon-based material wherein the carbon-carbon bonding is mostly of the graphite sp2 form. Sputtering is the preferred method to apply the coating. The preferred method is closed field unbalanced magnetron sputtering plating (CFUBMSIP). As one alternative, a metal-containing underlayer is very helpful for adhesion. This PCT document also discloses alternating layers of a metal-containing material and the carbon material. Preferred metals are chromium and titanium. Claim 9 discloses a first hard layer of a nitride, carbide carbonitride or boride and then a carbon layer. It seems that WO 00/55385 may address the broad concept of a hard layer-tribological layer scheme.
International Publication WO 99/27893 to Teer et al. [entitled CARBON COATINGS, METHOD AND APPARATUS FOR APPLYING THEM, AND ARTICLES BEARING SUCH COATINGS] discloses the method to apply the carbon coatings of WO 00/55385 discussed above. This document discloses alternating layer of metal-containing layers and carbon layers. Like in WO 00/55385, the WO 99/27893 document identifies chromium and titanium as the preferred metal components. The sputtering may also take place in a nitrogen atmosphere so as to form metal nitrides and metal carbonitrides. The focus is on a medical prosthesis.
European Patent 0 842 306 B1 to Teer et al. relates to metal-sulfur coating layers such as, for example, molybdenum disulfide. This patent discloses coating sequences of MoS2/TiN or MoS2/Ti. At page 7, lines 10-18, possible coatings are identified as follows: MoS2 directly on the substrate; a (usually thin) layer of Ti followed by a MoS2 coating; a (usually thin) layer of TiN followed by a MoS2 coating; a (usually thin) layer of Ti followed by a mixture of MoS2 with up to 40% titanium (MoS2/Ti layer); a (usually thin) layer of TiN followed by a mixture of MoS2 with up to 40% TiN (MoS2/TiN layer); a mixture of MoS2 with up to 40% titanium directly on the substrate; and a mixture of MoS2 with up to 40% TiN directly on the substrate.
U.S. Pat. No. 4,619,865 to Keem et al. (and U.S. Pat. Nos. 4,643,951 and 4,724,169) appear to disclose a multi-layer coating scheme in which there could be a hard layer and a lubricious layer.
U.S. Pat. No. 5,100,701 to Freller et al. appears to disclose a hard layer (e.g., titanium nitride) with pores. These pores are intended to receive solid lubricant (e.g., molybdenum disulfide).
In some instances the top lubricious layer may include a metallic additive. In this regard, top surface layers appear to have been formed by co-depositing molybdenum disulfide and titanium to cutting tools first coated with titanium nitride and titanium aluminum nitride (Fox, V. C., Teer, D. G., et al., “The Structure of Inproved Tribologically Improved MoS2-Metal Composite Coatings and Their Inductrial Applications,” Surface and Coatings Technology 116-119 (1999) 492-497). Along these same lines, the addition of a top surface layer of molybdenum disulfidetitanium to titanium nitride and titanium aluminum nitride coatings improved the life of high speed steel drills as compared to tools that only had a coating of titanium nitride or titanium aluminum nitride.
In regard to the lubricious layer, carbon and C/Cr films have been found to have good tribological properties (Yang, S., Teer, D. G., “Investigation of Sputtered Carbon and Carbon/Chromium Multi-Layered Coatings,” Surface and Coatings Technology, 131 (2000) 412-416. U.S. Pat. No. 5,268,216 to Keem et al. shows alternating layers of molybdenum disulfide and a metal (e.g., nickel, gold or silver). In addition, carbon nitride films CNx, have good tribological properties (Chen, Y. H., et al., “Synthesis and Structure of Smooth, Superhard TiN/SiNx Multilayer Coatings with an Equiaxed Microstructure,” ICMCTF 2001).
Heretofore, hard coatings have included one or more of titanium, aluminum and silicon along with nitrogen. These coatings have been used in conjunction with cutting tools.
Nanolayers of titanium aluminum silicon nitride have shown good properties for cutting tools (Holubar,P., Jilek, M., Sima, M., Surface Coating Technology 120/121 (1999) 184-188). These types of composite coatings have been formed by simultaneously co-depositing titanium (or titanium and aluminum) and silicon, and reacting it with nitrogen by a variety of methods described in a number of articles [see Shizzhi,L. et al., “Ti—Si—N Films Prepared by Plasma-Enhanced Chemical Vapor Deposition,” Plasma Chemistry and Plasma Processing, 12 (1992) 287-297; Dias, A. G., et al., “Development of TiN—Si3N4 Nano Composite Coatings for Wear Resistance Applications,” Journal de Physique IV, 5 (1995), 831-840; Veprek, S., et al., Surface Coating and Technology, 108/109 (1998); Holubar,P. et al.; Beensh-Marchwick, G., et al., “Structure of Thin Films Prepared by Cosputtering of Titanium and Aluminum or Titanium and Silicon,” Thin Solid Films 82 (1981) 313-320 and Rebouta, L., “Hard Nanocomposite Ti—Si—N Coatings Prepared by DC Reactive Magnetron Sputtering,” Surface and Coatings Technology 133-134 (2000) 234-239].
U.S. Pat. No. 5,580,653 to Tanaka et al. describes single layer coatings aluminum titanium silicon nitride and aluminum titanium silicon carbonitride used on cutting tools for improved wear resistance.
U.S. Pat. No. 6,274,249 to Brauendle et al. describes specific tools (carbide end mills) coated with single layer Me(C,N) where Me comprises titanium and aluminum, and optionally at least one element such as B, Zr, Hf, Y, Si, W, Cr.
U.S. Pat. No. 5,330,853 to Hoffman et al. discloses multi-layer titanium-aluminum-nitride coating scheme for cutting tools. Silicon may be an element in the coating.
Another example of a coating scheme comprises a layered composite coating with nanometer thick alternating layers of TiN (or TiAlN), and SiN. Owing to its improved hardness properties, a composite layered TiN/SiN coating is reported to have one-third the wear rate of TiN (Chen, M-Y. et al., “Synthesis and Tribological Properties of Carbon Nitride as a Novel Superhard Coating and Solid Lubricant,” journal and date unknown), Northwestern University.) The refractory layer may be further improved by incorporating the one or more of alloying elements Cr, Mo, Nb, Y to monolayer TiSiN, to TiN in multilayer TiN/SiN, and to TiAIN in multilayer TiAIN/SiN coatings.